1. Field of the Invention
The present invention relates to a corrosion-protected support element for a soil anchor, a rock anchor, a pressure pile or the like. The support element includes a support member composed of one or more individual elements. For providing protection against corrosion, the support member is at least over a portion of its length surrounded by a tubular casing or sheathing. The hollow space between the support member and the casing is filled out with a hardening material, for example, cement mortar. The support element is mounted in a bore hole and the support member can be placed in force-transmitting connection with the ground through a force transmitting region extending over at least a portion of its length by filling the bore hole with hardening material, for example, cement mortar.
2. Description of the Related Art
Structural members which extend into the ground, such as, soil and rock anchors which are subjected essentially to tensile forces, or pressure piles which are subjected to compressive forces, are used for introducing loads, for example, from structures, into deeper ground layers. Consequently, such structural members have over the length thereof at least one portion along which the tensile or compressive forces acting in the structural member are transmitted from the structural member into the ground. In the case of tension rods, this force-transmitting length is the so-called anchoring length in the depth of the bore hole. The area of the free steel length is adjacent the anchoring length and extends toward the opening of the bore hole. Along this free steel length, the tension member is freely extendable. In the case of pressure piles, the transmission of the compressive forces takes place essentially along the entire length of the pressure member. For transmitting these forces, the support member is usually placed in the respective area directly in bonding connection with a hardening material, for example, cement mortar which is filled into the remaining space in the bore hole. This hardening material ensures the connection with the bore hole wall and, thus, with the ground.
In structural members of the above-described type, which are not only mounted temporarily, such as, for temporarily securing an excavation cleading, but also permanently, the corrosion protection of a support member consisting of steel plays an important role. In addition to the admission of water and oxygen dissolved in the water to the steel surface and any occurring stray currents, the main cause of corrosion is the formation of macroelements. Accordingly, the most important corrosion protection measure is the provision of a casing in the form of a plastics material tube surrounding the steel support member over its entire length, wherein the plastics material tube has a high diffusion resistance and electric volume resistance. This plastics material tube forms the first barrier which also ensures the electrical separation between steel support member and ground and, thus, facilitates monitoring of the corrosion protection measure by means of an electrical resistance measurement. By pressing in cement mortar within and outside of the plastics material tube, an alkaline environment is produced as the second barrier against corrosion.
In a known soil anchor for permanent anchoring systems, the casing is composed at least in the area of the anchoring length of a ribbed jacket tube of plastics material. An additional plastics material tube having a smooth surface may be slid over the adjacent portion of the free steel length for maintaining the longitudinal mobility of the support member (German Patent 17 59 561). If the longitudinal mobility of the support member is ensured in a different manner, for example, by using so-called grease strands for the tension member, the ribbed casing tube may also be connected to a smooth casing tube at the transition from the anchoring length to the free steel length (German Company Brochure "DYWIDAG--Bericht", No. 11, 1982, pages 12-14). In all cases, the ribbing of the casing tube in the area of the anchoring length has the purpose of transmitting the forces from the support member through the pressing body in the ground past the discontinuity formed by the tubes. Analogously, this is also true for pressure piles (German Company Brochure "DYWIDAG GEWI--Pfahl", DYWIDAG-SYSTEMS INTERNATIONAL GmbH, D-8000 Munchen, 1987).
Aside from the fact that a joint of casing tubes at the transition from the free steel length to the anchoring length represents a weak point, the ribbed plastics material tubes which have been available in the past have been found to be susceptible to mechanical damage, particularly when the anchor element is introduced into the bore hole. This is because ribbed tubes have a smaller wall thickness than tubes having a smooth wall because of the manner in which ribbed tubes are manufactured. In addition, when the pressure occurring during pressing in material and elongations or displacements occurring during tensioning of tension rods frequently negatively affect the tightness of the casing tube and the electric volume resistance thereof.